Schedule of Market Values of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 109,677	$ 106,839	$ 116,697
Cash | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	669	612
International Developed | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,534	6,406
Emerging Markets | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,360	4,114
Core Fixed Income | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,719	23,782
Long Duration Fixed Income | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58,312	55,931
REIT Fund | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,216	2,212
U.S. Large Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,547	8,520
U.S. Mid Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,651	2,613
U.S. Small Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,669	$ 2,649